Java编程计算兔子生兔子的问题

public class exp2{
  public static void main(String args[]){
    int i=0;
    for(i=1;i<=20;i++)
      System.out.println(f(i));
  }
  public static int f(int x)
  {
    if(x==1 || x==2)
      return 1;
    else
      return f(x-1)+f(x-2);
  }
}

public class exp2{
  public static void main(String args[]){
    int i=0;
    math mymath = new math();
    for(i=1;i<=20;i++)
      System.out.println(mymath.f(i));
  }
 
}
class math
{
  public int f(int x)
  {
    if(x==1 || x==2)
      return 1;
    else
      return f(x-1)+f(x-2);
  }
}